The present invention relates to a drill pipe, a tubular drill string component for unconventional oil and gas drilling with 6⅛″ to 6¾″ production hole sizes. Unconventional oil and gas drilling is commonly referred to as shale drilling.
Shale drilling is becoming increasingly developed as hydraulic fracturing, or fracking, continues to make unconventional recoveries more efficient and economical. Shale drilling typically requires the drilled hole to include a vertical profile followed by a horizontal profile such that the well trajectory maximizes exposure to the production zone. A typical Bakken well profile would have a kick-off point between the vertical and horizontal profiles located at about 10,000 feet Measured Depth (MD) followed by another 10,000 feet MD of horizontal section. Typical build rates from vertical to horizontal are about 10 degrees dogleg or higher, increasing the well tortuosity and hence the cyclical stresses on the drill pipe.
Issues associated with conventional drilling are exacerbated in the case of shale drilling. Drilling horizontal wells is more challenging as the drilled lengths increase, both vertically and horizontally. Challenges include managing ECD (Equivalent Circulating Density), providing directional control towards the trailing end of horizontal section, efficient hole cleaning, and dealing with inefficiencies due to drill string buckling and increased tubular wear.
Horizontal drilling with a longer horizontal section tends to increase hole cleaning challenges, and can cause the drill string to get stuck if drilling parameters and mud properties are not closely monitored and adjusted in real time.
Difficult drilling conditions lead drill pipes used for unconventional drilling to have a shorter drilling tubular life than drill pipes used for conventional drilling. A typical shale well horizontal section is drilled with the drill string in compression, increasing contact between the pipe and the formation or casing, especially in curved portions, leading to wear. The life span of drill pipes used on shale wells is significantly reduced by 1-2 years from the typical 4-5 year life span of drill pipes used for conventional drilling. Drill pipes in shale wells thus require more frequent repairs, and more frequent replacement than conventionally used drill pipes, hence also driving the costs higher.
Currently used drill pipes typically have a 4″ outside diameter (OD), following standards described in the API SPEC 5DP: Specification for Drill Pipe, the entire content of which is incorporated herein by reference. Buckling and mid-section wear are two main issues associated with existing drill pipes, which are related to drill pipe diameter selection.